Jpn+pb



Filed July 20, 1956 11, 1966 w, c w ET AL 3,228,338

METHOD FOR INCREASING THE BURNING RATE OF PROPELLANTS 5 Sheets-Sheet 1 A L0 0 8 09 y 1/ w w ,2 I o v )r J I j! Z o 7 2/ r J 0.6 I bo 5 A 1 a:

o Z 0. T 2 II a: JPN+2% cu WIRE (0.005 mm.) a o- JPN-+2% cu WIRE (o.oo3"o|AM.)

A- JPN STANDARD 0.2

0 O O o O O O O O O O O O O O O O O O O Q m G) O N 1' 0 (a Q N m N BURNING RATE (IN/SEC) PRESSURE (PSIA D-DOUBLE O-DOUBLE BASE PROPELLANT BLANK BASE PROPELLANT .2% cu WIRE (o.oo5"o|AM.)

INVENTORS. JOSEPH COHEN "o o o o o o o 000 ALVIN s. GORDON 8 8 8 g g g g 8 5 WILLIAM s. MCEWAN PRESSURE (PSIA) {Md/Z. \LF M ATTOR NE YS.

Jan. 11, 1966 a CEWAN ET AL 3,228,338

METHOD FOR INCREASING THE BURNING RATE OF PROPELLANTS FilGd July 20, 1956 3 Sheets-Sheet 5 o w |.e U) I l6 v 2 f V I4 2 L2 3 0: 4 (D V E .0 I! m I a -omen ENERGY x-|2 STANDARD 0.3 V x-|2-+5% ALUMINUM 0 SPHEROIDAL GRANULES g X-I2+5% nomzzo ALUMINUM a: x-|2+5% ALUMINUM WIRE(.O20"DIAM.) In I I I I I U) 0.6

o O O O O O O O O O o O O o O O O O 0 o (D m N D O Q G) N O O N N N IO '0 I PRESSURE (PSIA) PROPELLANT WIRES INVENTORS.

JOSEPH COHEN ALVIN S. GORDON WILLIAM S, MC EWAN MM/Q \KF' W ATTORNEYS.

United States Pat ent 3,228,338 METHOD FOR INCREASING THE B RATE OF PROPELLANTS William S. McEwan and Alvin S. Gordon, China Lake, and Joseph Qohen, Arcadia, Calih, assignors to the United States of America as represented by the Secretary of the Navy Filed July 20, 1956, Ser. No. 599,279 1 Claim. (Cl. 10298) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method for increasing the burning rate of propellants.

Increase in the burning rate of propellants at operating pressure ranges is important in the interest of increased thrust, Burning rate increase has been obtained in the past by addition of reactants to the propellant compositions, construction of the propellant grain to furnish greater burning surfaces, in the case of solid propellants, and by other expedients, all of which have certain disadvantages. For example, the addition of reactants quite often undesirably alfects the ballistic and stability properties of the propellant, and construction of a propellant grain to provide greater burning surface requires expensive manufacturing techniques and reduces the strength of the finished grain.

The principal objective of this invention is to provide a method for increasing the burning rate of propellants which does not require a change in the composition of the propellant and does not involve increasing the burning surface of the propellant grain.

It is another object of the invention to provide a method as stated which is relatively inexpensive and which does not require complicated manufacturing techniques.

The invention comprises the incorporation of metal wires into propellent compositions. By propellent composition is meant one used for the propulsion of a jet actuated device and by jet actuated device is meant a device in which at least a part of the propelling force is furnished by the reaction of burning gases which are expanded through one or more nozzles. By double base propellant, as used in this specification and claims, is meant one in which the major ingredients are a high explosive such as nitroglycerin, diethylene glycol dinitrate, methyl trimethylomethane trinitrate or others and a suitable high energy polymer such as nitrocellulose. Increases in burning rate of propellants up to 22 percent have been realized by the addition of segments of substantially incombustible wires in accordance with the present invention. Metals which have been found suitable are copper, silver, aluminum, molybdenum, tantalum and lead. The principal requirements of the metal are that it be a good heat conductor and have a high melting point. While the effect produced is not completely understood in all its phases it is to a good first approximation for equal weight percent proportional to the thermal conductivity of the metals, the melting point of the metal, the radius of the wire and inversely proportional to the density of the metal. Since the result is due to a physical rather than a chemical phenomena, the invention is applicable in varying degrees to any propellant system.

The invention is best described by reference to the following description taken in connection with the accompanying drawings hereby made a part of this application, and in which;

FIG. 1 is a log-log plot of burning rate against pressure for a conventional JPN propellant before and after the addition of copper Wires of diilerent diameters;

FIG. 2 is a similar showing in which the propellant used is a conventional double base propellant having a low heat of explosion of about 850 cal./ gram;

FIG. 3 is a similar ty e comparative showing of results obtained on JPN propellant by the separate addition of tantalum, molybdenum, lead, copper, silver and alumi num;

FIG. 4 is a similar type comparative showing of results obtained by the separate addition of molybdenum, lead, copper, silver and aluminum wires to N-S propellant;

FIG. 5 is a similar type comparative showing of the results obtained by adding aluminum wire to high energy X-12 propellant; and

FIG. 6 is a cross section of a propellant embodying the invention.

The following examples are included for purposes of illustrating the invention but are in no way limiting thereof.

The JPN propellant used in the examples has the following composition: nitrocellulose-about 65%, nitroglycerin-about 25%, plasticizer, such as, diethyl phthalate-ahout 10%. The composition of N-S propellant is: nitrocellulose-about 50%, nitroglycerin-about 35%, diethyl phthalateabout 10%, stabilizer (Z-nitrodiphenylamine)about 2%, ballistic modifiers (lead salicylate and lead Z-ethyl hexoate)about 2.5%. In the examples the burning rate was determined by a standard technique. This involves the melting of a fine fuse wire threaded through a hole drilled through the propellant at right angle to the axis. When the fuse wire melts, a small current it carries is interrupted which stops an electric clock in the circuit. Three carefully spaced fuse wire stations are employed to get the burning rate. The results from this method agree very closely with photographic measurement of the burning velocity.

Example 1 Two percent by weight of copper wire .005 in diameter and one-fourth inch long was incorporated in JPN propellant having a calculated heat or" explosion of 1220 calories per gram, and the burning rate of the composition determined. For comparative purposes, the burning rate of JPN free of wires was also determined. Plots of the burning rate curves for each composition are shown in FIG. 1. As will be noted, an increased burning rate of over 22% was obtained by addition of wires to the propellent composition.

Example 2 Example 1 was repeated with the same propellant using 2 percent by weight (based on the weight of the propellant) of copper wire of the same length but of a diameter of .003, and the burning rate curve plotted in FIG. 1. An increase of 22% in burning rate is also indicated by the addition of this smaller diameter Wire to the propellent composition.

Example 3 Two percent by weight of .005" diameter copper wire 4" long was added to the following composition:

Percent Nitrocellulose 51 Nitroglycerin 35.1 Di-ethyl phthalate 11.9 2-nitrodiphenylamine 2.0

This composition had a heat of explosion of 850 calories per gram. A plot of the burning rate curve of this composition is shown in FIG. 2. This plot shows than an increase of about 22% in burning rate .was effected by the addition of wire.

Example 4 Separate compositions were formulated containing JPN propellant and wires of one of the following metals: tantalum, lead, copper, aluminum, silver, and molybdenum. Burning rate curves were made for each of the compositions and the results plotted in FIG. 3 with the plot of a burning rate curve made of JPN to which no wire had been added. A significant increase in burning rate is noted for the compositions to which wire was added. The wires of tantalum, lead and silver were .005" in diameter and 'those of copper and aluminum were .003" in diameter. Wires one-fourth inches in length were used and in an amount of 2 percent by weight of the propellant.

Example 5 Separate compositions were formulated containing N-5 propellant and wires one-fourth, inch in length of one of the following metals: lead, copper, aluminum, silver and molybdenum. The wires of silver and lead were .005" in diameter and those of copper and aluminum were .003" in diameter. Burning rate curves were made for each of the compositions and plotted in FIG. 4 with a curve for an N-5 composition free of wire. It will be noted that significant increases in burning rate were obtained in the pressure region above 1400 p.s.i. for the compositions to which wire had been added. The plot also shows that the addition of wire does not materially affect the ballistic property of the propellant, as evidenced by the fact that the mesa property is not destroyed by addition of the wires.

Example 6 Five percent by weight of aluminum wires one-fourth inch long and .020" in diameter were added to highenergy X-12 propellant having the following composition:

Weight Component: Percent Nitrocellulose 49.0 Nitroglycerin 40.6 Di-normal propyl adipate 3.3 2-nitro-diphenylamine 2.0 Lead B-resorcylate 2.5 Monobasic cupric salicylate 2.5 Candelilla wax 0.1

The composition had a heat of explosion of 1050 calories per gram. The burning rate curve of the composition was plotted in FIG. 5 with separate burning rate curves of the propellant to which (1) no wire had been added, (2) 5% of atomized aluminum was added, (3) 5% of aluminum wire was added and (4) 5% of aluminum spheroidal granules had been added. The greatest increase in burning rate is noted in the case of propellant to which wire was added.

The above results clearly illustrate the increased effect in burning rate produced by the invention. Further, the addition of wire to propellants does not undesirably affect the balla-stic properties of the propellant and does not affect its stability properties.

The examples show the operativeness of the invention with propellants having wide ranges of heats of explosion. For example, the heats of explosion of N-5 and that of the propellant used in Example 3 is about 850 cal./gm.,

4 while that of JPN is about 1200 cal./gm. and that of X-12 is about 1050 cal/gm.

All of the above compositions, with the exception of that of Example 5, were formulated with 65/35 acetone/ ethanol. They were mixed in a sigma blade dough mixer and extruded through a diameter orifice. After drying, the strands were inhibited with two coats of Vinylite and three coats of polyvinyl alcohol. The finished strands were of diameter. The copper Wire was wiped four times With an acetone soaked towel before it was cut and weighed.

While the invention has been disclosed by operative modifications which are limited in scope as to propellants, metals, Wire sizes and amounts, the scope of the invention is not so limited. While X-ray radiographic analysis showed that in the examples included herein the wires were not randomly oriented but tended to be oriented parallel to the grain axes, an efiect caused by the working of the propellant during the extrusion process in which diameter grains were formed, orientation in the direction of burning of the propellent mass is not critical. The effect of increased burning rate also occurs in large grains wherein there is random orientation of the wires, however, the effect is somewhat more noticeable when the wires are oriented in the direction of burning. The wire can be added up to amounts at which loss in energy due to displaced propellant over- 'comes the advantages derived from enhanced burning rate. A preferred range is up to 15% by weight of wire to propellant. If the nature of the wire is such that the molten material reacts slightly with products of combustion of the propellant matrix, then larger amounts of wire can be used. In the case of aluminum wire, for example, there is some reaction between wire and propellant which generates heat in addition to the heat conduction phenomenon. The length to diameter ratio of the wire segments is not critical.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

Double-base propellant compositions consisting essentially of about 44-60% nitrocellulose; from about 25- 45% nitroglycerin; from about 2-5% of a ballistic modifier selected from the class consisting of lead salicylate, lead 2-ethyl hexoate, lead fi-resorcylate, cupric fl-resorcylate, cupric salicylate, monobasic forms of the enumerated salts, and mixtures thereof; and from about 2-15% short segments of wires of metals selected from the group consisting of silver, aluminum, copper, lead, molybdenum, and tantalum.

References Cited by the Examiner UNITED STATES PATENTS 845,678 2/1907 Bayliss 5215 1,301,381 4/1919 Bucking-ham 10287 2,417,437 3/1947 Nicholas 10290 FOREIGN PATENTS 652,542 4/ 1951 Great Britain.

BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL BOYD, ARTHUR M. HORTON, SAMUEL FEINBERG, Examiners.

R. F. STAHL, Assistant Examiner. 

